1. Field of the Invention
This invention is directed to the art of drilling rock for heavy construction, oil wells, water wells, or mineral exploration holes or blastholes by rotary methods using compressed gas to cool the drill bit and to clear the borehole of cuttings.
More specifically, this invention is a device to reduce the flow of water entrained in the compressed gas to the bearings of the drill bit and to function as a check valve to inhibit the backflow of detritus and water into flushing air flow passages and open bearings of the bit following normal interruptions of compressed gas supply with the resultant plugging and contamination of drill bit components.
Compressed gas supplies are naturally laden with water. The compressed gas used in drilling, usually compressed air, is divided into two supply streams within the bit; one supply stream is used primarily to clear rock cuttings from the borehole by injecting this stream through at least one flushing air flow passage and nozzle and a second supply stream is channeled to the bearings to protect and cool the bearings of the bit. Water is deleterious to bearings, hence the life expectancy of the rock bit bearings may be enhanced by restricting the entrance of water with the cooling gas flow. Water is not a problem in the supply stream used primarily to clear rock cuttings from the borehole. The borehole may be flooded if it penetrates an aquifer. When the high pressure gas supply is turned off--as when drilling is interrupted for maintenance--and the borehole is flooded, water flows back through the open bearings and flushing air flow passages and up the drill pipe carrying rock cuttings. When the backflow ebbs, the cuttings settle and tend to plug or dam bearings and flushing air flow passages. When the gas supply is returned, plugged nozzles can inhibit cleaning, interfering with continued drilling. Contaminated bearings may fail prematurely.
2. Description of the Prior Art
U.S. Pat. No. 3,401,758 teaches use of a single, centrally-located check valve to serve more than one jet nozzle. The bearing supply system is isolated above the check valve and thus some fine abrasive slurry could be ingested into the bearings while the gas pressure above the valve is reduced. No attempt is made to restrict water flow entrained in the gas supply to the bearings.
The elevated temperatures generated by a rotating rock bit may be damaging to the elastic memory of the resilient member, upon which this valve depends for closure.
U.S. Pat. No. 3,788,408 concerns a water deflector intended to reduce the amount of water delivered to the bearings by way of the gas supply. A deflective cone is used effectively in one example, however, in other examples taught in the patent, the advantage is largely lost due to secondary back deflection and turbulent flow.